Hardware for counterbalancing of window sash
Curl springs formed of metallic tapes with a spring tendency to curl themselves into coils have a spring force that remains constant throughout their operating range, which makes them desirable for counterbalancing the constant force of gravity on a window sash mounted to move up and down within a window. An optimum way of arranging constant force curl springs is suggested in U.S. Pat. Nos. 5,353,548 and 5,463,793, and other arrangements of constant force curl springs are suggested in recent U.S. Pat. Nos. 2,262,990; 2,644,193; 3,992,751; 4,935,987; 4,953,258; 4,961,247; 5,232,208; and 5,661,927.
When sash shoes are desired with drop-in slots for receiving sash pins lowered into the shoes from above, as a removed sash is replaced in a window, curl springs counterbalancing the shoes must remain clear of a region directly above the shoes when they are locked in place in a shoe channel of a window jamb. This precludes shoe mounting of the curl springs as suggested in U.S. Pat. Nos. 5,353,548 and 5,463,793 and requires that curl springs be mounted in the shoe channels near the top of the window. Prior curl spring mounts that can accommodate sash shoes with drop-in pin slots are unnecessarily cumbersome and expensive. This invention aims at a low cost and effective mount for a plurality of constant force curl springs arranged in a shoe channel of a window jamb so as to provide the necessary clearance for a shoe having a drop-in pin slot.
Our invention meets these requirements by combining a simple and inexpensive mount for a plurality of curl springs with a low cost and effective way of connecting free spring ends with a sash shoe. A mounting block that can be secured in a shoe channel of a window jamp upholds two or three constant force curl springs loosely retained in the shoe channel. A lowermost curl spring rests on the block and has an uncoiled free end that extends downward past the mounting block to connect to a locking tilt shoe that supports a sash. A second curl spring is positioned in the shoe channel above the lowermost spring and has a free end extending downward past an opposite side of the mounting block to the sash shoe so that the two spring coils counterrotate against each other as the sash shoe moves up and down in the shoe channel. The single mounting block thus supports both springs in a way that avoids sliding contact between metal surfaces by simply counterrotating the spring coil peripheries against each other as the sash shoe moves up and down.
A third curl spring can be mounted above the second curl spring with the aid of a bearing block that separates the second and third springs so that a free end of the third spring can join the free end of the second spring in extending down past the mounting block to the sash shoe. The mounting block has at least one upward extension positioned to prevent any sliding metal contact between the outer periphery of the lowermost curl spring and the free end of the second spring passing downward alongside the lowermost curl spring.
Connections between the free spring ends and the sash shoe are made by striking barbs from the free spring ends so that the barbs lodge in widened recesses of slots molded into the sash shoe. The spring ends can be laterally inserted edgewise into the spring retaining slots of the sash shoe so that the barbs enter and interlock with recesses of the slots, and the spring ends are thereby held against vertical withdrawal from the shoe slots. Once the assembly is mounted in a shoe channel, walls of the channel retain the springs and the spring ends against any lateral withdrawal from the shoe slots.